The present invention relates to apparatus for regulating the temperature of a device whose temperature must be carefully controlled, and in particular, to an apparatus for regulating the temperature, and thus the frequency of oscillation of a crystal of a crystal controlled oscillator. The present invention operates in conjunction with a power supply of an electronic circuit, and thus generally relates to the field of power supplies also.
In many electronic circuits, the temperature of a component of the circuit must be regulated within precise limits. For example, in many circuits, a crystal controlled oscillator is used for providing the various clock frequencies required for timing and synchronizing purposes in the circuitry. In many instances, the frequency of operation of the crystal which controls the oscillator must be regulated within precise limits. For example, variation in temperature may affect the frequency of oscillation of the crystal. In order to maintain a stable temperature, and thus maintain the frequency substantially constant, a special heater may be provided to maintain the temperature of the crystal within a certain range. This however, is wasteful of energy since a larger power supply or a special power supply is needed to provide for the power requirements for the heater necessary to provide temperature compensation for the crystal. See, e.g., U.S. Pat. Nos. 4,396,892, 3,109,082, 3,413,438, 4,479,096, 4,157,466, and 3,158,821 as illustrative of the prior art.